Streak artifacts are known as one type of artifacts appearing in radiation tomographic images. Moreover, one type of the most representative streak artifacts is fine streak artifacts. The fine streak artifacts are a group of subtle linear artifacts generated in a specific direction and at a specific location.
Generation of fine streak artifacts is caused by the non-uniform geometry of a human body, and it is believed that one cause thereof is non-uniformity of the noise level across view angles or across detector channels in collected scan data.
In the prior art, there have been proposed a variety of techniques for suppressing such fine streak artifacts. One of the most general techniques is one directed to improvement of non-uniformity of the noise level by applying smoothing processing or the like to a portion of scan data in which the radiation detection level is low and the noise level is relatively high because of a long radiation penetration path and high radiation attenuation to reduce the noise level.